When a vertebra becomes damaged or diseased, surgery may be used to replace the vertebra or a portion thereof with a prosthetic device for maintaining the normal spacing of the vertebrae and to support the spine. The prosthesis, which may be referred to as a corpectomy device, is inserted into the cavity created when the vertebra was removed. One such device disclosed by Saggar, U.S. Pat. No. 5,702,455 includes a pair of cylindrical hollow members which are internally threaded and interact with a central cylindrical jacking screw which is externally threaded. The top part of the jacking screw is threaded in an opposite direction from a bottom part of the jacking screw. The jacking screw may be engaged and turned to adjust the vertical dimension of the device. When the jacking screw is turned, the hollow cylinders move either toward each other or away from each other.
Another prosthesis disclosed by U.S. Pat. No. 5,290,312 to Kojimoto et al. has two hollow rectangular cylinders. Each cylindrical part has at least one open end. The tubular parts are sized and shaped so that one part is telescopingly received in the other. The position of the parts in relation to each other are fixed by one or more set screws passed through apertures in one part to engage the other part. A corpectomy prosthesis disclosed by International Publication No. WO 92/01428 of Rasheed includes two parts, each having toothed surfaces. The position of the parts are fixed in relation to each other by the interengagement of the toothed surfaces.
Prostheses for supporting the spine after removal of a vertebra or a portion of a vertebra are desirably adjustable according to the size of the cavity created by the corpectomy procedure. The size of the cavity will depend upon the size of the particular patient, and the location of the cavity along the spine. In addition, the device may be adjusted either prior to insertion into the cavity or in situ within the cavity. For devices adjusted in situ, a convenient means for locking the device in the correct height is desirable. Although the patents discussed above present various solutions, further improvement in this area would be desirable.